This invention relates to electrostatic ink jet method and apparatus. More specifically, the invention relates to multiple nozzle ink jet devices of the type that employ continuous streams of drops that are selectively diverted from a gutter to a target.
Ink jet marking technology is attractive in today's world because it converts information in electrical form directly into a tangible form, e.g. black ink on white paper. Ink jet devices using multiple nozzles offer this direct conversion capability at very high marking speeds.
Multiple nozzle devices are implemented in three types of architecture. One type is disclosed by Lewis et al in U.S. Pat. No. 3,298,030. Another architectural type is disclosed by Sweet et al in U.S. Pat. No. 3,373,437. A third ink jet architectural type for multiple nozzle devices is that disclosed by Paton in U.S. Pat. No. 3,956,756.
The Lewis et al device is a character printer. It employs multiple nozzles in a linear array with each nozzle assigned the task of composing all the characters required in a column of characters on a page. Collectively, the nozzles print rows and columns on the entire page. This device is totally unable to record pictorial information.
The Sweet et al device is a pictorial printer. The printer it discloses can create a raster pattern composed of multiple rows of spots, dots or pixels that cover an entire page. As such, by selectively diverting droplets between a gutter and the page, in a binary yes-no fashion, a wide variety of pictorial recordings can be created. Typically, the nozzles are aligned in a linear array. The number of nozzles is equal to the number of pixels within a row of a raster pattern. By moving the printer relative to the page or target, the linear array of nozzles are able to generate the plurality of rows that make up the raster pattern. A principal drawback with the Sweet et al type of architecture is the difficulty of manufacturing the plurality of nozzles close enough together to give adequate resolution for images required in high quality reproduction applications.
The Paton type architecture is also a pictorial printer that records a raster pattern in a fashion similar to the Sweet et al type of device. The difference is that a given pixel density (pixels per inch, ppi) is achieved with a fewer number of nozzles. This is made possible by linearly deflecting the drop stream from each nozzle along the row of the raster pattern.
The device disclosed by Paton pertains to the textile art and operates at pixel densities not suited for what is generally understood to be adequate for high quality reproduction work. The misalignment between the nozzles and the pixel positions, inherent to all multiple nozzle devices, imposes a serious limitation on the ability of a Paton type device to record information with an acceptable degree of accuracy and at a high enough quality level. One reason is that the drops in a Paton device are electrically aimed at an ideal pixel location rather than mechanically as with a Sweet et al device. In textile manufacturing, the Paton type of device is merely repetitively generating an aesthetic design and is not hampered with the restraints required when reproducing a message.
Accordingly, it is a primary object of the present invention to overcome the limitations of the foregoing types of multiple nozzle ink jet devices.
Another object of this invention is to design a high quality, high resolution pictorial ink jet printer.
A further object of the invention is to align the drops in traces of one nozzle relative to all the other nozzles in a multiple nozzle device of the type in which each nozzle covers a given number of pixel positions in the row of a raster pattern.
Yet another object of this invention is to employ drop position sensors adjacent a multiple array of nozzles designed to cover a given number of pixel positions in a row so that a raster is faithfully recorded.
The above and other objects of this invention are realized by locating drop position sensors adjacent an array of nozzles that sweep out traces to cover the pixel positions in a row of a raster pattern. Two position sensors are provided for each nozzle and, in a presently preferred mode the sensors are located so that adjacent nozzles share sensors. The sensor spacing relative to each other is of critical importance. The sensors are positioned on a common substrate with a high degree of accuracy and as such are like a surveyor's benchmark. The drops from a nozzle are charged so as to fly exactly under the sensors. First the drops are positioned under one sensor and then another. The nozzle in question is thereby charge amplitude calibrated relative to its two sensors or benchmarks. The other nozzles are similarly calibrated. Because the sensors are accurately aligned to each other, a fortiori, the drops from the calibrated nozzles are accurately aligned to a row of ideal pixel positions on a target.
The present multiple nozzle device is referred to as having the drops from its nozzles "stitched" together. The term "stitching" refers to aligning electrically the electrostatically deflected drops issued by a plurality of nozzles relative to ideal pixel positions on a target.